Anti-Ice Systems - Cruise Performance Penalties
 

For aircraft equipped with anti-ice systems which rely on bleed-air offtake from the engines, I'm trying to understand how the associated performance penalties with these systems switched on (I'm thinking about the increased fuel burn for the same speed/altitude) are dealt with during cruise flight planning.
Do aircraft ODM's/Performance Manuals include an optional allowance for anti-ice being on/off?
Or, is this not a flight planning issue because you don't plan to remain cruising in icing conditions?
Regards
WUT

At cruise altitude, when the temp is below -40 deg C, you do not suffer from icing so only need to consider anti-icing in the climb and descent. If you wish to you could carry extra fuel but contingency fuel is normally more than adequate to cover both wing and engine anti-iceing.

At least that is the case on my aircraft.

Assuming that you can cruise at such altitudes. Things get a bit more interesting with various unusual dispatch cases or en route failures which may impose altitude limitations (either by rule or due to performance limits)

The ODM for the Dash 8 specifies the penalty for having de-icing on. For long range cruise you increase power by 1.5% which gives an increase of 8 lb/hr fuel flow per engine. For max cruise the airspeed will be 2 kts less. I don't think anyone's going to worry about 2 kts or 8lbs/hr of fuel when flight planning.

Wind up...

As "Don Coyote" mentioned it is unlikely you will have icing conditions at -40 while at cruise altitude.

But if you have a faulty anti valve quite often the MEL proceedures will require the Valve locked in the OPEN position. (this also results in HPSOV being locked shut)
With the anti ice valve being open it results in an extra air load on the engine resulting in a poofteenth of a percent extra fuel burn.
eg RB211-G is about 0.3 % extra fuel

Hope this helps

MBolt

Thanks very much for the help folks.
WUT

The turboprop world can spend a whole flight in icing conditions.

Happy memories of chugging along in an ATR watching strange shapes grow on the ice evidence probe.....

I seem to recall we didn't apply a cruise fuel penalty, but did assume a small difference for holding fuel (8 kg an hour instead of 7 rings a bell). IIRC this was more to do with minimum speed. Its fading into distant memory though.

CPB

B717-200 with BR715 engines.

• Engine Anti-ice ON - add 50kg/hr fuel flow.
• Engine Anti-ice & Airfoil & Tail Anti-ice ON - add 125kg/hr fuel flow.

Anti Ice deltas
 

IIRC, in the performance charts in the flight crew operating manuals of some types, the figures for fuel burn are given as a function of altitude, mach number and gross weight, but there is a box with deltas to be applied for various bleed configurations - pack flow high, anti ice on etc. Can't remember what sort of values the deltas are though.